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What is the process to get a simulator FAA certified for IFR training?
Assuming I've got the hardware and software that meets the FAA requirements for a BATD (Basic Aviation Training Device), what is the process I would go through to get the simulator certified?

The FAA Advisory Circular 61-136 contains the guidance for Aviation Training Devices, including the BATD's.
The AC states that as long as the system has been FAA approved by the manufacturer (and in your case you say that it "meets the FAA requirements"), that no specific approval is required for training conducted under 14 CFR 61.  For use under 14 CFR 141 however, you would need specific FAA approval (see below).
14 CFR 61 Approval
You must simply follow the conditions specified in the AC:

5. APPROVAL OF BATD FOR USE UNDER PART 61. To be approved for use for pilot   training and certification under part 61, a BATD should:
a. Be capable of providing procedural training in all elements for
  which it is to be used.  Those elements should be specified in an
  acceptable training curriculum or as specifically  authorized by the
  FAA and meet the description and suggested criteria outlined in this
  appendix.
b. Have the following documents available for inspection by the
  student and instructor:

The list of ATD components as required by paragraph 3c,
A copy of AFS-800’s letter of approval and authorized use of the ATD, and
A copy of the QAG for the ATD being used.

c. Successfully pass the start-up self-test described in paragraph
  8c(2). If the device is being used in a course of training for a pilot
  certificate or rating, a person authorized by the FAA to provide
  ground or flight instruction should observe this test. After the ATD
  self-test is complete, no other software of any kind may be started on
  the computer running the ATD software.
d. Remain in the approved configuration during the training session.
  Authorized ATD  instruction may not proceed after a malfunction of the
  ATD system has occurred. The operator  must correct the ATD
  malfunction and repeat the start-up test described in paragraph c of
  this section before resuming authorized instruction. In addition, a
  BATD may be used in a training curriculum that provides for:

A similar scope and content of a syllabus that is used under part 141;
Instructional materials for flight events;
A means of showing progress, such as an outline of stage (phase) checks and criterion  levels of performance; and
The authorized use as approved in the AFS-800 letter of approval.

14 CFR 141 Approval
141 Approval is almost the same, but must be approved by the school's POI (principle operations inspector):

6. APPROVAL OF BATD FOR USE UNDER PART 141. Local FSDO may approve  BATDs as part of an overall part 141 curriculum approval and
  certification process. Pilot schools that want to use a BATD as part
  of their training curriculum must notify their principal operations
  inspector (POI). The POI is responsible for approving how the BATD is
  to be used in the certificate holder’s part 141 curriculum. To be
  approved for use under part 141, a BATD should:
a. Be capable of providing training in all elements in which it will
  be used, as specified in the syllabus, and meet the description and
  suggested criteria outlined in this appendix.     b. Have the
  following documents available for inspection by the student and
  instructor:

The list of ATD components required in paragraph 3c,
A copy of AFS-800’s letter of approval and authorized use of the ATD, and
A copy of the QAG for the ATD being used.

c. Successfully pass the start-up self-test described in paragraph 8c
  of this appendix. A  person authorized by the FAA to provide ground or
  flight instruction should observe this test. After the ATD self-test
  is complete, no other software of any kind may be started on the
  computer running the ATD software.
d. Remain in the approved configuration during the training session.
  Authorized ATD  instruction may not proceed after a malfunction of the
  ATD system has occurred. The operator  must correct the ATD
  malfunction and repeat the start-up test described in paragraph c of
  this section before resuming authorized instruction.
e. Be used in an integrated ground and flight training curriculum
  which provides for:

The scope and content of a curriculum in compliance with part 141,
The authorized use as approved in the AFS-800 letter of approval,
Instructional materials for flight events, and
An outline of stage (phase) checks and criterion levels of performance.

Careful! The above and 'approved' answer is not correct! FAA Approval is required for a BATD! As the Advisory Circular says:

Manufacturers of devices meeting the guidance and standards in this AC
  will receive a document from the FAA Flight Standards Service’s General Aviation and
  Commercial Division, AFS-800, approving them as either a BATD or AATD with an
  accompanying authorized use statement.

You need to get the AFS-800 approval after an extensive review of the QAG. This can take anywhere from 6 months to a year currently in my experience for even a school building a simulator. I have yet to meet someone who has truly certified a home build system.
Appendix 2 says:

b. To request FAA approval of a BATD, manufacturers should send approval requests to:
  (1) By regular mail: FAA Flight Standards Service, General Aviation and Commercial
  Division, Certification and General Aviation Operations Branch, AFS-810, 800 Independence
  Avenue, S.W., Washington, DC 20591.
  (2) By e-mail: (call (202) 267-8212 for e-mail instructions).
  NOTE: E-mail, with attached text format documents, is the preferred
  correspondence method.
  c. The request for approval must include a QAG

Here is an example link to one of the older approval documents that expires in 2019:
https://flyelite.com/downloads/faa/pi135.pdf


text:
Can throttle control be considered as a primary flight control?
My flight instructor asked me if throttle can be considered as a primary flight control?

14 CFR 23.673 - Primary flight controls defines primary flight controls as:

Primary flight controls are those used by the pilot for the immediate control of pitch, roll, and yaw.

While a throttle could be used to effect changes in aircraft attitude (depending on configuration and other factors), the effect could hardly be called immediate/direct. So, throttle could hardly be called a primary flight control; and as @Ron pointed out, there are gliders.
Note: I'm aware that aircraft have been controlled solely using throttle. But it is an exception rather than the norm.

You mean you don't have thrust vectoring engines?

Yes, according to wikipedia, the throttle is considered to be a primary flight control, along with

a control yoke (also known as a control column), centre stick or side-stick (the latter two also colloquially known as a control or joystick), governs the aircraft's roll and pitch by moving the ailerons (or activating wing warping on some very early aircraft designs) when turned or deflected left and right, and moves the elevators when moved backwards or forwards
  rudder pedals, or the earlier, pre-1919 "rudder bar", to control yaw, which move the rudder; left foot forward will move the rudder left for instance.
  throttle controls to control engine speed or thrust for powered aircraft.

It is considered to be a primary flight control because it makes a big difference to the aircraft, a plane with no throttle can't fly!

"a plane with no throttle can't fly" Except pretty much every glider...

@RonBeyer I guess so, I was just focusing my answer on powered aircraft

While they say that Wikipedia is pretty reliable these days, I'd take aeroalias' quoting of CFR as a higher authority. Of course, OP doesn't specify which country he's in, so US-FAA may not have authority, but I'd imagine that's a pretty standardized definition.

@RonBeyer: Except for a bungee launch, even gliders need a throttle to get into the air. It cannot be wished away completely.

according to Wikipedia I'm sorry, Wikipedia is wrong. It is useful, but has never been an authoritive source of information. (Someone here should go and edit it!)

@PeterKämpf: that's hardly an argument to say that a throttle is a primary control in a glider!

@PeterKämpf Probably splitting hairs but I wouldn't count a glider without it's own motor (motorglider) as having a "throttle" when being towed. The throttle is owned by the tow plane and part of that aircraft primary control system, not the glider :)

@RonBeyer: A glider isn't flying (it is incapable of maintaining altitude and airspeed simultaneously in still air), it's falling with style.

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text:
Flying coworkers with a commercial pilot's license (USA/FAA)
I will soon have my commercial pilot's license, and work full-time in a company and role unrelated to aviation. As a private pilot under FAA part 61.113b, I know that I can fly myself to conferences or sales meetings while having my employer reimburse me for the aircraft rental because the flight is only incidental to my employment.
My boss asked if my new CPL will allow me to take coworkers on such a trip, and I don't know how to answer him. It would be incidental to my employment and for a common purpose (i.e. I am also attending the same meeting), and there is no holding out since it would only be employees of the same company for a common purpose. I am also salaried, so there is no additional direct pay for the flight (just logging time). I'm not sure how to answer, and there are 3 scenarios to further complicate this (assume all aircraft have had 100-hr inspections):

I rent the plane and submit for reimbursement along with my other ordinary business expenses.
The company seeks out and rents the plane without my input.
The company rents the plane from an FBO, but after asking me for a recommendation on where to find one.

Which of these are permitted with a CPL? I'm 99% sure that #2 is completely fine, but can't find regulations for or against the other scenarios.

Definitely related, possible duplicate: Would this “being paid while flying” scenario be considered “flying for compensation”? (Make sure to check out the answers, not just the question.)

Since you have a CPL, you can receive compensation for flying.
Your question and concern is over the means of reimbursement which may have implications beyond that of the FAA. That said, I'm not a lawyer and I would suggest your company consult with one and establish a policy. Most companies I've worked for prohibit personal flying incidental to the business specifically due to liability concerns.
To avoid confusion, I would stick with option 1) as that makes it clear it's your choice to fly and not that of the business. If the company rents the plane, it may expose the company to additional FAA regulation as well as liability and tax implications.
As a point of explanation; before I retired from the USAF it was not uncommon to use private aircraft to travel on TDY (Temporary Duty - the military version of a business trip). The rules under AF regs and the Joint Travel Regulations (DoD) allowed you to travel using a privately owned aircraft or a rented aircraft. IIRC the AF required a CPL/IR and a total of 200 hrs. The rules also specified what expenses were allowed and how they were to be reimbursed.
If you used your own aircraft, it was classified as POV (Personally Owned Vehicle) travel. That was no different than driving your own car on the trip. In that case you were reimbursed at the POV mileage rate. That rate when I was in was actually less than the IRS allowed mileage rate and wouldn't come close to covering the cost. It also didn't matter if anyone was travelling with you, be it a coworker or family member.
If you rented an aircraft, it was treated the same as if the company allowed you to rent a car to make the trip. You were reimbursed your actual rental cost (wet) up to the cost airfare for the trip for all persons travelling together. What that meant was that if you traveled alone, the reimbursement was typically less than the rental cost (say \$400 for airfare vs \$600 rental). If you had two or more travelers, the airfare typically exceeded the rental cost and the entire rental was covered. The limitation was that only coworkers on travel orders counted towards the reimbursement.

A simple, but not comprehensive, way of looking at it is:

Who supplies the plane?
Who supplies the pilot?

Not examining all circumstances, if you work for the company, and one of the things they pay you for is flying, that makes things easy.
If the company supplies the plane, (whether they own it, lease it, or rent it, with or without your input) that makes things easy.
So assuming that your boss asks you to fly for the company, and the company provides the plane, things look good.  However there are are few more details.  Your company should have their risk management people take a look at it, primarily from an insurance standpoint.  Also, you should consider negotiating with the company for checkout and recurrent training.  This way you can readily get some paid time in the plane, and get things like IPC or other currency rides accomplished at company expense.
I have flown many fellow employees in corporate aircraft.  If they are experienced, I put them in the right seat (we have a couple of U-2 and one older SR-71 pilot on staff), even if they are a private pilot.  I brief them and make clear what I expect from them.
You may wish to enhance your knowledge and skills when flying others. I have a dotted line to the corporate flight department, which is very helpful. Sounds like you may not have that, but you want to expand your skills on handling people, first aid, etc. My chief corporate pilot suggested that I take CPR, survival courses, etc. which I took advantage of. Never needed them, but I have flown globally in very remote areas, and having that training was nice.

"we have a couple of U-2 and one older SR-71 pilot on staff"!!!! wow. Must be interesting times 'round the water cooler with those chaps.

Very few stories about those flights.

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text:
Why do we feel gravity on a plane?
How come a plane flying at constant velocity experiences gravity?  If you were in a space capsule flying (not accelerating) you would feel weightless until you hit the ground.  Why not a plane?

Hi Chris K. It's usually a good idea to wait a day or so before accepting an answer on Stack Exchange. Accepting an answer, while it doesn't prevent adding additional answers, signals to the community that you feel your question has been answered satisfactorily, which can result in it receiving less attention from the community than it otherwise would.

Isn't this a better question for the Physics SE site?

If you're in a plane and you don't feel gravity, you're in deep trouble.  Unless you're on a dedicated microgravity flight.

obligatory XKCD: https://what-if.xkcd.com/58/.  You have to go sideways really fast to continually miss the earth as its gravity pulls you in a circular path (which we call an orbit).

The surface of the earth at the equator is travelling around the center of the earth at roughly 1000 miles per hour. Why do you feel gravity standing on the equator?

@MichaelKjörling so? If he feels it was answered appropriately then let him do that.

It is really, really annoying that people are mentioning vomit-comet like flights.  Of course, obviously, in this "popular science puzzler", the OP is asking about ordinary level flight.

@TheGreatDuck Of course, and as you will note, OP has not unaccepted the accepted answer. That is absolutely their choice. However, OP should also be aware of the potential consequences of early answer acceptance.

hi @Shufflepants.  the exact answer to your question, is given in my answer below.

@Fattie that was a rhetorical question referring to the OPs claim that a plane travels at constant velocity. It was to point out a flaw in their logic. There was no need to address the question.

If you were in a space capsule not accelerating you would feel gravity... The only reason you don't feel gravity in orbit is because your capsule/spaceship/whatever is falling as fast as you are!

Even with "not accelerating" means "not using rockets", it is not true that "If you were in a space capsule flying (not accelerating) you would feel weightless until you hit the ground." At least, that is not true if the ground you hit is Earth, because Earth has an atmosphere. If you crash into the Moon instead, you'll feel weightless until the final impact, but in that location an airplane is just a capsule with useless slabs of metal sticking out from the sides.

@Shufflepants because you need to be going about 20 times faster to not feel gravity while standing on the equator.

@jmarkmurphy I'm aware of the reasons. I was posing the question to Chris K to get him to think about his own question in a different way. And the answer "you need to be going faster not to" doesn't really answer what I think is his fundamental misunderstanding about how gravity works and the necessary conditions for feeling weightless are.

Wouldn't this be better in the Flat Earth SE site?  Why isn't there a FE SE site!  It's all a conspiracy sheeple!  Why does a plane that flies straight ever hit the firmament?

From a Newtonian (non-relativistic) viewpoint, this question contains an incorrect statement: "If you were in a space capsule flying (not accelerating) you would feel weightless until you hit the ground. ".  That's not right.  In a weightless trajectory, there is an acceleration, unless the spacecraft is at a point where the net gravitational pull on the spacecraft is exactly zero.  The key is that there's no acceleration component other than that induced by gravity.  If this situation were to arise in an aircraft, it would be called "falling" (or the trajectory of the "Vomet Comet".)

Except that we now understand that the "Newtonian" perspective is incorrect. All frames of reference are equivilent, (equally valid). Some are just more useful than others. Gravity is itself a fictitious or psuedo force, only necessary in force balance equations because we generally measure motion in a non-inertial, (accelerated) frame of reference.

Please read Wikipedia https://en.wikipedia.org/wiki/Fictitious_force

This is the difference between flying and in orbit. In orbit, you are indeed falling toward the earth, but the spacecraft is too, and you're going fast enough that you keep missing the earth.
In an aircraft, because it's staying aloft due to lift, it is not falling. This is why you experience the pull of gravity on a plane.
Some aircraft are designed to feel weightlessness, see Vomit comet.

Well if you're not falling and the sum of all forces is zero then wouldn't you still be weightless?

@ChrisK: In an aircraft in level flight, you're are still affected by the force of gravity. The aircraft's lift is pushing you the opposite direction. If the sum of all forces is zero, is means you are in equilibrium, meaning you are not being accelerated in any direction; it does not mean that you are "weightless".

Actually, one should say that the force, you feel in an aircraft is not a gravity but the floor (seat etc.) pushing against you. You never feel gravity per se, you feel forces on your body which counteract gravity pull. In the orbit, there is still gravity pull on your body, of course, but spacecraft is not pushing against it, so therefore the weigthless feeling.

@Martin brilliant explanation, thinking this way around is SO much easier in certain circumstances!

@ChrisK: You, as a human, would fall to the ground. The plane, however, generates lift that keeps the plane up. Since you are in the plane, the plane stops you from falling. The force the plane enacts on your body to stop you from falling is what you call "feeling gravity". A capsule in orbit, however, has no lift, and the vehicle is in free fall just like you are. Since the vehicle doesn't enact a force on your body you don't "feel" gravity. But make no mistake, even people in orbit are subject to gravity, they just seem to be floating due to their frame of reference with the capsule.

@ChrisK: Think of the vomit comet. When the plane is almost in free fall (and your body is too), it looks like you're almost weightless (relative to the plane, which is your frame of reference). Being in orbit is sort of like being in that freefalling plane, but you never hit the ground because you keep missing it.

@Martin: That simple comment is the perfect answer, if you'd like to post it...

@LightnessRacesinOrbit OK, you have it there. :) It feels quite similar to other answers already posted, but well. I can always delete it later.

@ChrisK: Keep in mind: when you just stand on the ground, you're also not accelerating and the sum of all forces is zero! If the ground were not in the way, pushing up on you with normal force opposite your weight, you'd fall. The plane is the same, it is in the way of you falling and pushes you up. The forces which the object you stand on uses to itself be stationary (be it normal forces passed on by the rocks below resisting compression [on the ground], or lift [in a plane], or even tension [an elevator]) is immaterial. As long as gravity exists, some force must oppose it for you not to fall

@ChrisK "Well if you're not falling and the sum of all forces is zero then wouldn't you still be weightless?" The only way to feel weightless is to be falling.

@Martin: Don't know whether others agree, but I find value in perhaps the same facts being presented in multiple ways. After all, that's why the software allows multiple answers on questions that originally (on SO) were intended to always be objective fact.

You cannot feel gravity. It is not a real force. It is what is referred to as a "fictitious" or psuedo force. Only there because you are examining things in an accelerated or non-inertial frame of reference. What you actually feel is the aerodynamic force pushing on the aircraft, that is accelerating the aircraft upwards to match the 1G acceleration of the frame of reference you are measuring everything in. Look at this Wikipedia article: Fictitious force Fictitious force - Wikipedia https://en.wikipedia.org/wiki/Fictitious_force

Why do we feel gravity on a plane?

Exactly for the reasons we feel gravity when traveling on a train:

We're not free falling (the cabin floor prevents this to happen).
We're not at orbital speed which is about 28,460 km/h.
We're not flying very tight curves that could create a free fall (but only for a few seconds anyway).

Gravity and weight
Everything is weighty everywhere in the cosmos as soon as it is subject to some acceleration (e.g. gravity acceleration, but not limited to it) and it tries to oppose this acceleration.
So there are only two means to escape gravity acceleration effects:

Remove gravity with another exactly opposite acceleration. This is "the satellite way". The satellite own speed and its circular trajectory create (as viewed from the satellite) a centrifugal acceleration exactly opposite to gravity acceleration. Effects of both accelerations disappear.
Remove everything preventing gravity to fully act, this is "the free fall way". Gravity wants us to fall, then we just remove everything preventing us to fall, starting with the floor and/or the ground. When we jump from some height we're in micro-gravity for a short time, and then at the hospital if we underestimated the time. This is also what some aircraft do for 30s to train astronauts ("0G flight"). While the gravity still exists, its effects are cancelled by accelerating with the "gravity flow".

In both cases, the aircraft and the satellite experiences "micro-gravity" (which means a residual gravity in the order of some $\small \mu g$). Any mass subject to micro-gravity is (nearly) weightless.
For the physicists here, there is actually a single case, as a satellite in orbit is also in free fall and there is no centrifugal force, provided we select the appropriate frame of reference for the observer (an inertial frame). If we wanted to be even more rigorous, Einstein also intuited gravity is actually fictitious (if I may say) itself, an idea which led him to the discovery of the general relativity and the space-time curvature
Constant velocity vs constant speed

How come a plane flying at constant velocity experiences gravity?

Micro-gravity never happens in a trajectory at constant velocity.
The reason is because constant velocity is constant speed and also constant direction:

Constant speed means we are not free falling, else we would accelerate towards Earth.
Constant direction means we are not creating any centrifugal acceleration either, because it requires changing direction.

When satellites are in circular orbit, they are not at constant velocity, they are at constant speed.
Following their orbit, the direction of their displacement is constantly adjusted, hence velocity constantly varies, which allows them to create a centrifugal acceleration exactly opposite to gravity.
Can we create micro-gravity on a plane (or on a train) moving horizontally?
Horizontal doesn't mean "in straight line". It means at right angle from the direction of gravity (the local vertical), so when moving horizontally on large distances, we are actually following Earth curvature.
If the plane/train follows Earth curvature (hence changes direction constantly), we could in theory achieve micro-gravity, but at the condition we travel very fast, a bit faster than the ISS (27,560 km/h at the current time), about 28,460 km/h. In such case we are in orbit at altitude zero (orbital trajectory doesn't depends on altitude).
This is not possible in practical, an enormous amount of power would be required and everything would melt due to friction.
Micro-gravity in a plane flying a specific curve
But as explained in Can one fly up side down while a glass of water keeps full due to g-forces?, we can create micro-gravity by flying a specific trajectory. In that case, the speed we are missing is replaced by constant changes in direction along the curve. This gives nice videos, like the funny weightless dog with the two unperturbed guys:

Source

To sum up
Weightlessness is the consequence of being subject to micro-gravity which can be obtained:

At constant speed we need to follow a curve which creates an acceleration exactly opposite to gravity. This either requires moving at a large and specific speed (orbital speed) or doing relatively tight turns at limited speed.
In free fall we must follow the downwards trajectory and permanent acceleration dictated by gravity, which means, e.g. in 35 seconds, and 6 km lower, we are already moving hypersonic! Not so comfortable, and that's only for the first 35 seconds!

For feasible and durable micro-gravity at low altitude, the two techniques must be combined.

"Orbit doesn't mean absence of gravity" It's even more brutal than that; orbits are not possible absent gravity. When you are in an orbit, you are following a curvature formed by the interaction of velocity and a gravitational field. This is why you end up with seemingly odd results like spacecraft travelling in a straight line, but not in the reference frame you're used to.

This should be the accepted answer IMO

Satellites are also free-falling. They do not create new forces.

@MichaelKjörling - Well, an unpowered orbit is not possible absent gravity (or some other force, like magnetism). :-)

@T.J.Crowder If it's powered, I'd argue that it's not an orbit; rather, that's being on a powered trajectory with continuous or non-continuous trajectory changes, with the trajectory possibly forming a closed ellipse. (Not saying that doesn't have its uses; look at Rosetta's trajectory around comet 67P.) Good point though on "some other force", but since in our universe gravity is pretty much ubiquitous, well...

I don't think this answer uses the term "microgravity" correctly. For example, microgravity won't keep water in a glass. "Free fall" also is used in a way that I think is potentially confusing--the satellite also is said to be in free fall, but that means something very different from all but the first few instants of a parachute jump.

You never actually “feel gravity” at all†, not in orbit, not on a plane and not on solid ground either.
What you do feel on ground is the earth pushing against your feet, with a force that exactly cancels out the gravitational acceleration. As soon as you stop that force, e.g. by cutting the ropes in an elevator, the gravitational acceleration would very quickly change your velocity, downwards, which of course inevitably brings you back to the ground (where it will hurtfully reaffirm its upward force...) in situations like an elevator. We're completely used to that upwards force as the normal state, so much that we don't even notice it as a force and instead talk about the “gravitational down force”, but physically that's not really the force that's there.
In a plane, the situation is much the same: the force you're feeling is the force of air flowing around the wings, pushing the entire plane upwards. Without that force, the plane quickly stops travelling at constant velocity and instead travels ever faster towards the ground.
Now, for a space capsule in orbit, this actually happens as well: here, there isn't any force counteracting the gravitational acceleration, so it is in free fall. But because it has a blisteringly fast horizontal velocity, there's not enough time for it to fall down onto the ground – it “misses the Earth” instead, and thus continues its orbit.

†The only place where you could actually feel gravity itself is close to a black hole, where your body would be getting stretched out by the tidal forces... but that never happens in homogeneous gravity field, and any sufficiently large/distant field is approximately homogeneous.

Spaghettification is still one of the best terms to come out of modern astronomy!

Not entirely true. The inner ear can sense which way is up, also called the sense of balance. Still, whether we experience it or not, the question still seems to be about a real force that exists.

@Octopus No, neither your inner ear can sense gravity. It just feels from which side are floating particles in the ear supported by the ear channel, which is, in turn supported by your body, which, in turn by the floor or seat of an airplane. All your "sensing" is nothing more than strain/deformation of some of your tissue. Homogeneous force field only does not cause any deformation.

@Martin, your argument is completely semantic. The OP has already pointed out that a plane passenger feels something and a space capsule pilot does not. Call it not gravity if you like, but there is a sensation!

@Octopus It can be seen as semantic one, but I believe, it is better way to think about situation. If you imagine completely empty space (so totally no gravity), only with your chair (and some capsule or so, so you do not suffocate :) ) which will exert exactly the same force on your body like when you are sitting at your desk at home, you will get exactly the same feeling of "gravity" despite there is no real gravity. (yes, you can state that it is because gravity/acceleration equivalence, and you will be right, still inner ear is no way special part of your body here).

@Octopus, no, not semantic at all. Ask JFK Jr. Oh wait, he's dead. Because he couldn' t feel which way is up. No one can, no matter what the OP said. This fact (myth) has killed many many pilots, and their passengers, (Kobe Bryant). We call it unintended flight into IMC.

We are, the speed is not sufficient for this to be easily observable. We are actually a little bit lighter while in a plane, because it is also circling the Earth, just like a spaceship does, but even for SR-71 at top speed (assuming 3540 km/h = 983 m/s) the effect is too small to be sensible:
$$ g = \frac{V^2}{R} = \frac{(983\frac{m}{s^2})^2}{6400000 \ m} = 0.15 \frac{m}{s^2} = 0.015 \ g $$
(g is close to 9.8 on Earth). It is even not really minor, but I doubt if 0.015 g acceleration is very observable. For Boeing 747 (assuming 988 km/h) this is only 0.0011 g.

Of all the answers, this is the only one which points out that there is a smooth shift from feeling gravity (i.e. 1g) to feeling weightless (i.e. 0g), and provides the equation that you can use to calculate how much acceleration you feel.  In fact, this effect can play an important role once you go faster than the SR-71, into the realm of hypersonic aircraft.

So with a 747, we are about 1% lighter?  Who-hoo!

@chux If your 747 is accelerating straight downwards at 1% of gravity.

@immibis Who-Noooo!

Like @Cort Ammon suggest, this nicely answees with a formula. I recommend adding a calculation of the speed aplane would need have to be in orbit at a common flight height of like 15000 feet

It is not a gravity, you feel, but the floor (seat etc.) pushing against you. You never feel gravity per se, you feel forces on your body which counteract gravity pull. In the flying airplane these forces come from wings' lift, but in the orbit, there is no such counterforce, so you feel weightless despite gravity is till there.
All the feeling of weight comes to your brain from various strain or deformation sensors in your tissues. So in order to feel weight, there has to be force deforming your body. Homogeneous gravity field (gravity around Earth is homogeneous enough for these purposes) exert exactly the same force on each single point in your body, therefore causing no deformation.
On the other hand, floor, seat etc. supports your body locally only and the force needs to be "distributed" through your body, which causes strain in the tissues and "feeling of weight".

This captures what I was going to write into an answer: the concept that we call "weightlessness" is really an internal property: it is the absence of these distributed forces.  It actually doesn't matter at all whether they are caused by true weight (i.e. the effect of gravity pulling each part of the body down), or if it is caused by another effect (such as centripetal acceleration in many amusement park rides).

An aeroplane flying does not fly fast enough to become weightless. A person inside an aircraft flying at constant altitude becomes weightless if the centrifugal$^1$ force F$_C$ = $( m \frac{V^2}{R})$ from following the curvature of the earth equals the force from gravity ($m \cdot g$).

$$ m \cdot \frac{V^2}{R} = m \cdot g \Rightarrow V = \sqrt {R \cdot g}$$
With g = 9.81 m/s$^2$ and R = 6,400 km even at cruise altitude, we get V = $\sqrt{9.81 \cdot 6.4 \cdot 10^6}$ = 80,000 m/s. At that speed 10 km above the earth's surface, you'll be weightless
$^1$ makes for an easier to understand graphic.

"An aeroplane flying does not fly fast enough to become weightless." Well, not in level flight. It's perfectly possible to experience 0 normal force in accelerated flight. This will not be the most comfortable experience for the passengers, though.

An excellent and perfect answer.

@reirab - something to consider.  If the plane is simply falling (the vomit comet), (you and I understand that .....) that's a totally different "junior physics popular science topic" to understand, than the worthwhile "junior physics popular science topic "why astronauts in orbit feel weightless"..... it's a shame to conflate those two (interesting but different) "junior physics popular science topics" - IMO !

FWIW koyovis - "An aeroplane flying does not .. become weightless"  Actually IMO an aircraft in normal level flight is, in fact, precisely weightless.  Using the usual "weight V. mass" ! high school definition of those two terms.  Note that in it's own frame of reference, if you hung the 747 by a scale - it would weight zero.  (You would have to, obviously, have another chopper or something pacing it, just underneath, to weigh it using a large bathroom scale, to be in it's frame of reference. Of course, it would weigh zero.  As would (say) a balloon-type craft at vertical rest.)

@Fattie Orbit is 'simply falling.' The reason for feeling weightlessness is the same in both cases - namely, there's no normal force pushing up on you to oppose the force of gravity pulling you down. That is, you're in freefall (accelerating somewhere between 0.9 and 1.0 g toward the center of Earth) in both cases. The only difference between them is that the orbital craft is also moving sideways fast enough to continually fall around the Earth, whereas the airplane isn't and would eventually experience a very abrupt upward force exerted by the ground if allowed to continue its fall.

hey @reirab, right - as working mathematicians you and I both know that.  But they're two different "popular science topics" - you know!  Just IMO. It's enough to explain why being "in a 747" is different from "in the ISS" !

Consider the "vomit comet" flights, where they intentionally fly the same plunging path that a bowling ball would "fly" if gravity took it.  If you simply continued that flight path, you would go SPLAT.
Wings are a funny shape, specifically to create lift.  That is so they can create a flight path other than that one.
The "gravity" you feel on the plane is the wings doing their thing.  The wings themselves have been adjusted to counteract gravity exactly, so the force feels the same as gravity.  The reason to counteract gravity exactly is to remain at the same altitude, the one ATC assigned them so they don't hit other aircraft...
... Or (this is a little more complicated) remain at a constant rate of climb/descent for passenger comfort and simplicity.  If you are moving at a constant speed, acceleration is zero, and gravity is an acceleration effect.

The answer to this question could not be simpler.
At a given altitude, you need to be going a certain speed, to achieve "weightlessness".
At sea level, that speed is 28,500 mph.
At 30,000 feet, that speed is 28,400 mph.
In an airplane, you are not going fast enough.
That's all there is to it.
You are not going fast enough.
(Note that exactly the same could be said of a train or car. If you were going 28,500 mph in a TGV, you would get the "weightless" effect. You would float around, etc, inside the TGV exactly as astronauts float around inside a space station.)
Use this calculator, to know the speed you need for different altitudes:
http://www.calctool.org/CALC/phys/astronomy/earth_orbit

XKCD covered this in detail. While the other answers cover all the physics angles, XKCD does a great job of bringing the science down to an easy-to-understand level (emphasis mine)

Gravity in low Earth orbit is almost as strong as gravity on the surface. The Space Station hasn't escaped Earth's gravity at all; it's experiencing about 90% the pull that we feel on the surface.
To avoid falling back into the atmosphere, you have to go sideways really, really fast.
The speed you need to stay in orbit is about 8 kilometers per second. Only a fraction of a rocket's energy is used to lift up out of the atmosphere; the vast majority of it is used to gain orbital (sideways) speed.
This leads us to the central problem of getting into orbit: Reaching orbital speed takes much more fuel than reaching orbital height. Getting a ship up to 8 km/s takes a lot of booster rockets. Reaching orbital speed is hard enough; reaching to orbital speed while carrying enough fuel to slow back down would be completely impractical.

The fastest aircraft ever, the X15, couldn't stay in orbit because it only traveled at about 2km/s, or 25% of the necessary speed.

Newton's Cannonball.
https://en.wikipedia.org/wiki/Newton%27s_cannonball
In a plane, you're the cannonball marked "A", and the only thing stopping you from plummeting straight into the ground is the lift generated by the wings.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Is there any particular reason the A380 doesn't have a centre wing tank?
Today I learnt something new, but apparently the A380 has no centre wing tank, which leads me to ask, is there a specific, design reason for this? Or did Airbus just think those huge wings were big enough to hold all the fuel they'd need?
Although, I've heard rumours that the A380F if built would have had a centre tank (no idea how true this is), but this shows the engineering is possible, Airbus just chose not to go with it for the passenger version. Any reason why?

Im not going to vote but this question may air on the side of "mostly opinion based" as unless an Airbus engineer speaks up or there is some document stating so it may be all speculation.

As the wings can hold all the fuel this is preferred over a center wing tank since the weight of the fuel reduces the loading on the wing. The lift force acts opposite of the force created by the weight of the fuel due to gravity. This effect reduces the forces at the wings root.

Also the A330-300 standard model doesn't have a center tank, while the  -200 and A340 do.

It simply doesn't need one. Depending on the source, the A380 has a range from 8200 NM1 to 8477 NM2. The current longest scheduled flight is AKL-DOH, which is 7848 NM3. So the current configuration is capable of flying any of the current routes.
As far as the A380F, it really wouldn't make sense to add a center tank there either. The extra fuel weight would mean less cargo capacity available.
 1 Wikipedia
 2 Aerospace Technology, 11/19/2013
 3 Wikipedia

It would not affect cargo space. There's no way you can put cargo into the center wing box with all the structural elements it holds.

@user71659 I was thinking weight-wise, but I was looking at diagrams and there's currently a hydraulics bay in the wing box. I don't know what it looks like in there, but a center tank might require a pretty hefty redesign and displace that forward into the forward cargo bay. I'll clarify, though.

Distance in square or even cubic nanometres? Cool :)

@Zeus Fixed it. It was supposed to be in cubic New Mexicos

Note that A380 (as most large aircraft) is already weight-limited. It can't take full load for the maximum range.

The A380 simply does not have enough space left on the lower deck, which is why they moved all the fuel into the wings. That is likely the reason for the poor performance of the A380, as the wings turned clumsy and produce a lot of drag, which than again requires a large empennage.
With an A380F, where you do not have crew accomodations on the lower deck and no "luggage" to be placed there, you would have enough space. So you could install a center fuel tank and add stream lined wings, but that would mean new wings just for the A380F, which is a way pointless.

The wings were clumsy to fit in an 80m wingspan to fit in existing airport infrastructure. The 'not enough space' argument doesn't add up: as an engineer, you choose what space you use for what purpose. Lastly, putting in a center tank increases the bending moment on the wing roots, so I highly doubt moving fuel to a center tank would make for more aerodynamic wings.

#1 The A380 has a center wing box just like any other aircraft (otherwise the wings would rip off). This section, which the A380 does have, is what would be utilized as the center fuel tank, just like every other aircraft.
#2 If the wings were aerodynamically "clumsy" and produced a lot of drag the aircraft would burn too much fuel, so no airline would fly it.
#3 The short distance from the CG to the empennage creates a short moment arm, requiring larger tail surfaces.  This is why the short 747SP has extended vertical and horizontal stabilizers- to compensate for the shorter moment arm.


text:
Can the pitch be very different from the angle of attack?
How much the pitch (horizontal orientation) can differ from the angle of attack? I am trying to understand the claim that "angle of attack indicator was unfortunately not available", contributing to problems during Air France Flight 447. Attitude indicator most likely was available?

angle of attack is in relation to the flight surfaces (wings) while pitch is the entire craft

yes, but since the "fligh surfaces (wings)" are fixed in one place to the "entire craft," AOA can be measured anywhere on the aircraft, and in fact AOA probes are not attached to the wings at all

http://i277.photobucket.com/albums/kk76/batcave777/A330_Probes_Location_F-GZCP_2009-06.jpg

The pilot would have had to combine the information from the artificial horizon, forward airspeed and rate of descent to guess the angle of attack. Not so easy in a stress situation.

@copper.hat: Angle of attack is a simple function of airspeed and weight (and vertical acceleration)!

@copper.hat: The pilots don't need to guess the angle of attack, they only need to keep it in safe limits. With airspeed that is trivial. Without it, they should train maintaining safe combination of pitch, vertical speed and power (but in AF447 they failed to do that).

@ratchetfreak: No, the important different is that pitch is relative to horizontal and angle of attack is relative to velocity relative to air.

@JanHudec: The AoA (along with pitch, roll, control deflection, etc.) is the solution of a differential equation and is certainly not a simple function of airspeed and weight. In steady state conditions the AoA may be a expressed function of airspeed (depends on the equilibrium manifold), but it is not a simple relationship. For example, AoA can be changed quickly due to either pilot input or external conditions while the airframe dynamics are much slower to respond.

@JanHudec: My comments were in regards to Flight 447, where the static pitot stopped worked for a while causing many issues. My point was that it would take a very astute crew to figure out the angle of attack from the artificial horizon, etc.

@copper.hat: Lift is proportional to alpha (below stall) and square of indicated speed and lift is equal to mass times vertical acceleration. Neither is differential equation. The pilots can feel the vertical acceleration and should be able to fly the plane close to equilibrium.

@JanHudec: It is impossible to discuss these things in comments and I suspect we are using some terms loosely. For example, I can have zero vertical acceleration, the same airspeed and weight and a different angle of attack. Just fly a really tight level turn and compare to level flight. The AoA of the former is higher, this is why accelerated stalls are an issue. Also, 'feeling' the vertical acceleration in a Citabria, Cub or whatever is a lot different than in a 200+t aircraft.

@copper.hat: Yes, we are. So I'll be explicit: Acceleration is the value measured by accelerometer on board (so relative to free falling frame of reference, in straight flight the value is 1 g) and vertical is in airframe coordinates (because lift and AoA are as well). I hoped it will be obvious from the relations.

The angle of attack is the angle between the wing (wing chord to be precise) and the direction of travel (undisturbed airflow). The angle of pitch is the angle between the main body axis and the horizon. The difference can theoretically be any angle, but during normal flight it will be limited to about 15 degrees.
The reason that the angle of attack sensor was inoperative was due to low airspeed. Below 60 knot IAS the indication is unreliable and therefore the indicator is inhibited. This also inhibits the stall warning. This lead to the confusing situation that lowering the nose to correct the stall increased the airspeed beyond 60 knots, thereby reactivating the stall warning.

The Angle of Attack indicator was not inoperative, because there is no such thing. The Angle of Attack sensor was operative, but it's output is only used for the alpha-protection (which was inhibited due to lack of airspeed) and stall warning (which was inhibited below 60 kias), but it is not shown in cockpit. It was shown, there would have been no reason to inhibit it; pilots know it is not useful on the ground.

Sure there are AoA indicators.  What have you the impression they don’t exist?

BEA acknowledged the unavailability of AoA indicators in the cockpit could have been a contributing factor, and recommended to assess the need to add them in the future. AoA indicators were only optional, and AoA information was accessible to the crew only after a voluntary disconnection (or failure) of the 3 ADR (BUSS demonstration on Youtube).

@CarloFelicione, some aircraft do have AoA indicators, but A330 is (or was at the time) not one of them.

It can be. Remember that the angle of attack is the angle between the chord line of the airfoil and the relative wind. Imagine if the plane is level with the horizon with zero airpseed. It will fall straight down, putting the angle of attack close to 90 degrees with the pitch close to zero.
That said, during normal flight it's not likely that pitch and angle of attack will be excessively different. But honestly the two aren't closely related: You can exceed the critical angle of attack and stall at any pitch, bank, or yaw angle.

Just want to add the image.
Angle of attack is relative to the direction of relative wind (which is equivalently relative to the direction the plane is going, if in still air and the angle of incidence = 0, i.e. the wing is mounted parallel to the longitudinal axis of the plane), while pitch is relative to the horizontal axis. Angle of attack depends on the pitch, current velocity of the aircraft and the wind. They can be different.
Angle of attack is important to the aerodynamics (amount of lift, drag, etc.), while pitch tells you the aircraft's orientation relative to the ground.
Image source
Assumptions for the image: still air and angle of incidence is 0.

+1. It's nearly correct, but the AoA isn't between the trajectory of the plane and the longitudinal axis. You need to add the angle of incidence. The chord line is not parallel to the longitudinal axis. This incidence angle is the mounting angle of the wings, and can be about 5°.

in addition to what mins said, you also have to consider that the relative wind might come froma direction slightly different from the plane's trajectory, as there might be actual wind to be summed to the aircraft velocity vector.

@mins, actually, it depends. Angle of Attack of the wing is measured from the chord line, but given that many aircraft have twisted wings, it seems pretty common to measure it from the longitudinal axis for the airplane as a whole.

@JanHudec: Wouldn't that be better to use the MAC rather than the longitudinal axis?

@mins, better for what? The zero lift line does not coincide with the MAC anyway, so you'd still have some $C_{L_0}$, so it makes more sense to just use the longitudinal axis and skip the addition of angle of incidence.

Just before the ground impact
Just watch this video of a looping gone bad during a flight display. At 1:30 into the video it becomes painfully obvious by how much both can diverge in extreme situations (shown above).
The flight path angle is the difference between pitch attitude and angle of attack. If pitch attitude and angle of attack would be equal, the airplane could only fly straight ahead at the same altitude. Once it climbs, it has to increase pitch attitude at constant angle of attack. With enough thrust or speed, both can be 90° apart.
Now consider flying inverted: Both are almost 180° apart.
In a dive, again the difference will become large because the flight path angle takes on negative values.
The more fun it makes to fly an aircraft, the more both angles diverge. Only boring aircraft will keep both of them at similar, low values.

"Now consider flying inverted: Both are almost 180° apart."-- what do you mean by this?  When I think of flying inverted the first thing that enters my head is sustained inverted flight.  Let's say the aircraft is designed for aerobatics and has a symmetrical airfoil with zero incidence.  What would a typical angle-of-attack be in sustained inverted flight, maybe minus 10 degrees?

Whatever the number is, wouldn't the pitch attitude just be that same number times minus one (so positive 10 degrees in this case, because the aircraft is pitched 10 degrees nose-to-sky.)  So that's a difference of 20 degrees-- nowhere near 180 degrees. Even if we double the angle-of-attack to 20 degrees we just get a difference of 40 degrees, nowhere near 180 degrees.

@quietflyer: Guess what definitions are for! They are meant to clarify what we are talking about. You are free to define your pitch angle differently from everyone else, but then please accept that your opinion will lead to different results. And the results of others aren't necessarily wrong only because you choose to pick a different definition.

Kampf: can you clarify your comment?  I'm not following.  How am I defining pitch attitude different from everyone else?  For example, what would be the pitch attitude according to the standard definition, of the aircraft in sustained inverted flight as described in my comments above?

How much the pitch (horizontal orientation) can differ from the angle
  of attack?

270 degrees appears to be the maximum angle that the pitch attitude can differ from the angle-of-attack.
Some examples of extreme differences between pitch attitude and angle-of-attack:

Jet fighter or aerobatic airplane or aerobatic glider in a prolonged vertical climb.  (May be a steady-state situation or the aircraft may even be gaining airspeed or it may just be a "zoom" climb where airspeed is exchanged for altitude; obviously only the latter is possible with the glider.)  For simplicity assume a symmetrical airfoil.  Pitch attitude is 90 degrees, angle-of-attack is zero degrees, for a difference of 90 degrees.
Now the throttle (if present) is pulled back to drop the engine power to zero, but the nose is kept pointing straight up until the aircraft starts to tailslide backwards.  Pitch attitude is still 90 degrees, but angle-of-attack is now 180 degrees, for a difference of 90 degrees.
Now imagine the tailsliding aircraft experiences a slight variation in angle-of-attack-- perhaps due to a horizontal wind gust striking the aircraft-- that changes the direction of the relative airflow by one degree, so that the relative airflow is aimed slightly toward the top surface of the wing, rather than aimed directly at the trailing edge.  Now the angle-of-attack has changed from 180 degrees (which also could be called minus 180 degrees) to minus 179 degrees.  Now the difference between angle-of-attack and pitch attitude is 269 degrees.
Flat spin with flight path approximating a vertical descent.  Angle-of-attack may be close to 90 degrees, but pitch attitude may be close to zero degrees.  Actually on the retreating wing it would seem the angle-of-attack may go beyond 90 degrees (wing actually moving backwards relative to the airmass, so the local airflow comes partly from behind), in which case the difference between angle-of-attack of that wing, and pitch attitude of the aircraft, would also go beyond 90 degrees.


text:
Why are the cockpit displays swapped between the captain's and first officer's sides?
This question focuses on Airbus, like the A320, but is not restricted to those aircraft as the situation seems to be the same for other aircraft.
In front of the left seat, the navigation display is displayed at the right of the the primary flight display, and it is the inverse of the right seat.
Is there a technical reason to do so? An historical one?

It's hard to see from the angle that your example photos were taken from, but the main reason is that they want the primary flight instruments (which are on the PFD, or Primary Flight Display) directly in front of the pilot, no matter which seat they are in.
The PFD gives the most critical information which is used to actualy control and fly the aircraft, so is designed to be in the pilot's direct line of sight.
Less critical information is put on the MFD (Multi Function Display).  Since the pilots sit close to each side of the cockpit, this usually means that there isn't room to place the MFD on the outside of the PFD.  Even if there was room, the extra display is used partially for redundancy, so they don't want to put it further away from the other pilot.
Since the PFD is directly in front of each pilot, it doesn't take any effort to switch between seats because of that aspect.
This photo (it's night, so a little dark but I think that you can see what I'm referring to) was taken from my head level while sitting in the right seat, which should make it pretty clear:

own photo

I'm not sure if cockpit displays are swapped between the pilot and copilot. Usually, the pilot (or for that matter copilot) will have their PFD (Primary Flight Display) right in from of them, with the navigation (and other) displays on their side. My guess is that this is the reason the displays appear symmetric.

Source: www.avweb.com
This photo, though from a helicopter (Bell 412) clearly shows the pilot and copilot PFDs right in front of them, in the same line as cyclic and between the rudder pedals.

Source: latinairforces.blogspot.com
Also, note that the information displayed could be switched between the two displays. Usually one display always shows the important flight info (i.e. acts as the PFD) while the other can be changed to show what the pilot wants.

It has to be symmetric because otherwise you would have to have a different arrangement of controls on either side.
The shape of the console is different left to right, so, for example, there is more room in the center of the panel than the outer edge. Everything is arranged to fit efficiently into that space. To use the same arrangement on the other side of the panel, everything has to be flipped mirror image.
It would be bad to have different arrangements of controls in the two positions, because it would be confusing to the pilots. Sometimes pilots sit in one seat, and other times in the other. They should have the same basic arrangement of controls in both cases.

Your answer is self contradictory: The symmetry is exactly what leads to a different arrangement of controls between the pilot & FO seats. i.e. [PFD] [MFD]---[MFD][PFD]. If the controls were arranged the same on each side [PFD] [MFD]--[PFD] [MFD], they would no longer be symmetric.

@FreeMan I think you are misunderstanding my statement. I consider a symmetry around the vertical axis to be the same "arrangement".


text:
Can espresso be made at cruising altitude?
Espresso makers work by bringing water to a certain temperature (typically 198-202°F / 92-95°C), and then extract it at a high pressure (~9 bar). Given that the FAA requires that cabins are pressurized to ~7,500 ft, this results in a few problems I can see.

The pressure differential between the boiler and the cabin would be very large. I fear that this would result in the espresso machine being compromised.
Water would boil at a much lower temperature (198°F / 92°C) resulting in the machinery not working correctly.
A sudden depressurization of the vessel could certainly result in a dangerous pressure differential resulting in explosive decompression.

Although, a Boeing 787 has a higher pressure cabin, in a typical airplane, could you safely brew espresso? Are there any FAA, or other safety regulations preventing you from doing so?

Expresso makers for aircraft galleys. One at B/E Aerospace.

The machine works with 9 bar (no, decent espresso works with 14). Sea level pressure is, by definition 1 bar. Pressure in the cabin is about 0.7 bar. 0.3 bar is completely insignificant compared to 9 bar.

@mins, is it espresso, or just filter coffee machine? I believe most airlines use the later, which does not use pressure anywhere.

An airplane cabin is pressurized to 8000' or less during cruise.  There are people that live at higher elevations than that and they make espresso with no issues.

If we can make an espresso in space I think we can make on at cruising altitude :)

@casey: Example: This espresso shop in Leadville, Colorado is at over 10,000 feet.

@JanHudec for the reason you mention I see no risk of damaging the equipment, but at 0.7bara the boiling point of water is 90C.

@steveverrill, yes, and coffee should not be made with water hotter than that anyway.

@JanHudec the question specifically states 92-95C. If that is right, the boiler thermostat should be adjusted. See my answer.

@DavidGrinberg -- ISS is pressurized to approximately sea level atmosphere.

Simply use espresso powder.

The pressure differential between the boiler and the cabin would be very large. I fear that this would result in the espresso machine being compromised.

The pressure in the espresso machine is 9 bars, 14 in a good one. The difference in outside pressure is 0.3 bars. That is comparably tiny value that does not make any practical difference.

Water would boil at a much lower temperature (198°F / 92°C) resulting in the machinery not working correctly.

Coffee should not be made with boiling water anyway. 198°F / 92°C is sufficient for making coffee.
Besides, if the boiler was pressurized, the water would not boil until way higher temperature (it isn't, but it does not heat the water above boiling point at that pressure).

A sudden depressurization of the vessel could certainly result in a dangerous pressure differential resulting in explosive decompression.

The pressurized content is water, not vapour, so it would not significantly expand if the machine cracked. After all, its pressure is relieved as part of normal operation (when the coffee drips to the pot) and it does not expand.
And its amount is tiny compared to the total volume of the aircraft anyway. Very tiny, because the pressure is only in the pipe from the pump to the ground coffee.

But that all assumes the coffee machine is espresso, which most of them are not. Usually they will be just filter machines where the water flows by gravity at ambient pressure or perhaps at some pressure, but much lower than in a real espresso machine. I believe some airlines do advertise they serve true espresso though.

The pressure in the espresso machine is 9 bars, 14 in a good one. The difference in outside pressure is 0.3 bars. wut?

@Federico mean sea level pressure is 1013 mbar, an 8000' cabin is roughly 750 mbar.  That is 263 mbar or 0.26 bar difference between sea level and an aircraft cabin at cruise.  0.3 is on the high side, but demonstrates at worst case it doesn't matter for the espresso machine.

@casey, but that's not what the question is about. The OP is not worried about the difference in outside pressure (1013 vs 750) but in water vs cabin (14 atm vs 0.75 atm)

@Federico yes, and that figure demonstrates that delta p at sea level is 13 bar and delta p in the cabin is 13.25 bar, a 2% difference and one the espresso machine won't even notice.

@casey, oh, I see the point now. thanks.

Sorry, but I had to butt in. :-) Espresso is extracted at 9 bars. No, even a good espresso machine doesn't use more. The source of the misunderstanding is that many manufacturers state what pressure the pump inside the machine is capable of providing (which is, naturally, higher than the normal pressure used). The pressure is regulated somewhere between 9 to 10 bars when the espresso is actually brewed, depending on the individual setting of the machine in question.

@Federico: there is no constant 9 bar pressure in an espresso machine, it's not a pressurized container of any sort, so there is no safety risk. The pressure is only present while the machine is actually pushing the water through the ground coffee. A sudden escape of pressure would result in hot water squirting from the machine that can scald somebody standing very close but will not pose any risk to aircraft safety.

The high pressure in the modern espresso machine is not created by the highly pressurized boiler. It is created by the pump pushing hot water under pressure. Many models do heave the boiler to foam the milk, for instance, but this is not required for making the coffee itself. This pump can even be hand operated. Some machines even need no electricity, just a hot water.
If exactly boiling water is required, it can be kept only slightly pressurized. However water under cabin pressure is also quite hot; maybe it is enough just to add more coffee or increase the brewing duration.
I am not competent to issue "airworthiness certificates" for espresso machines, but as a passenger I can say that the idea may be worth exploring; coffee as it is served now is never the best part of the flight experience.

Right - but, it is kept warm, and then usually driven by a pump, or a piston (potentially driven by hand). There is still the fear / problem that near the portafilter, there is a ridiculous amount of pressure. I've heard of retail espresso machines being fatigued, and resulting in explosions.

@SargunDhillon, 14 bar is great deal of pressure. But 14.3 bar is only 2% more.

@SargunDhillon Well, the difference is whether you have litres of high-pressure liquid, or 50 millilitres of high pressure liquid (enough to make an espresso). I think that a well-made machine will survive plane's explosive decompression without exploding itself. It's more the time (and price maybe) constraint that makes airlines use filter: it takes about the same time to make 3 espressos as to make a kettle of filter coffee.

Unfortunately, the accepted answer is off the mark. :-)
Espresso is extracted at 9 bars, even in so called "good" or "decent" espresso machines. The source of this misunderstanding is that most manufacturers state the rated pressure the pump inside the machine is capable of delivering (and consumers are often led to believe that bigger is better). The pressure is regulated to 9 bars when the espresso is actually brewed (with slight differences possible depending on the individual service setting of the machine in question). There is a pressure relief valve that simply sends the excess back to the water tank. Espresso coffee extraction is an equilibrium of many factors, including quantity, temperature and time. It's actually not even desirable to have a higher pressure than the traditional, tried and tested 9 bars, together with all the other standard parameters used.
What's more important in the context of the question is that an espresso machine is not a pressurized container of hot water. The 9 bars are created by a pump that only operates while the machine is actually pushing the water through the ground coffee. The amount of water is rather small (a serving of espresso is 30 ml, it's usual to have two-cup sprouts, meaning 60 ml). In any event of breach of pressure (eg. the portafilter accidentally knocked off), the pressure will fall immediately because it is only built up against the ground and packed coffee, nothing else inside the machine. With no resistance, the pump simply continues to deliver hot water, like a tap. So, the result could be a small amount of scalding hot water for anybody standing close, which is a nasty thing but certainly no risk to general aircraft safety.
Actually, it could be added that using a boiler to keep any amount of hot water is more characteristic of the traditional espresso machines used in catering and by connoisseurs at home. The kind of machine more likely to be used on board of an aircraft, the so-called superautomatic type (this is the combined machine that grinds the beans and brews the espresso at the touch of a button) tend to use heaters that simply heat the water flowing through them during the brewing process. This reduces the startup time of the machine and requires less electricity, although it produces espresso of lesser quality.
Because of this setup, the pump would deliver the same pressure at any flying altitude. It's the pressure relief valve that actually decides the pressure, not the pump. If it stays set at 9 bars, that's what will be used during the brewing process. What the altitude would influence is the temperature we can heat the water to before it starts to boil.
Espresso brewing needs to avoid boiling water at the usual ground level primarily because of the temperature limit of 100°C. It's not the boiling itself that would ruin the espresso (apart from the fact that steam, being compressible, would not work in a pump set up to send high pressure water through the coffee puck) but the high temperature: the aromatic ingredients in the coffee bean can only be extracted, exactly as the OP has stated, in a rather narrow temperature range and going near or above 100°C simply ruins the taste. In this respect, if ambient pressure differences would decrease the usable temperature range at higher altitudes (say, 92°C being the highest temperature of water that can be achieved before boiling), this would only require a different selection of coffee on board, one that tastes good when extracted at that temperature (probably meaning that both the composition of the blend and the roasting process should be adjusted accordingly but this task would be simply left to the supplier).

As the boiling point of water at 0.7bar absolute is 90C, there would be one small difference.
The specific enthalpy of water at these conditions is 376.783kJ/kg and the specific enthalpy of vaporization is 2282.81kJ/kg.
Assuming the machine heats the water to 95C, it will reach a specific enthalpy of 398.017kJ/kg, an excess of 398.017-376.783 = 21.234kJ/kg. There will therefore be flash boiling of 21.234/2282.81 x 100 = 0.93% of the coffee by mass. Although that doesn't sound much, water expands 2461 times when boiled under these conditions. So the volume of steam produced will be 2461 x 0.0093 = 22.89 times the volume of the coffee.
As I understand it, the water in an espresso machine is boiled under pressure at 9 bar and then forced through the coffee and released at ambient pressure. If this is done without adjusting the thermostat on the boiler, significant boiling will occur due to the pressure drop, possibly causing over-agitation of the coffee and / or vapour lock (inability of water to enter due to the volume of steam.) I can't drink coffee for medical reasons so I'm no expert on coffee, but neither of these sounds like a good thing. The thermostat on the water boiler should be adjusted below the boiling point of water.
I understand good quality espresso machines have an independent boiler for generating steam. That should be fine and can be left untouched.
As others have said, the difference between 1 bar and 0.7 bar ambient is of no consequence for the boiler if it normally operates at 9 bar. There is some possibility of erosion of water valves if superheated water flashes to steam within them due to the drop in pressure.

The pressure isn't in the boiler, it is between the boiler output and the coffee grounds / portafilter gaskets.  If you operate the machine without the portafilter it water just flows out of the boiler at ambient pressure.  The pressure is built up by the tamping of the coffee grounds and the portafilter gasket.  The pump will only push hard enough to push water through that.   If the water was boiled at 9 bar pressure it would have a temperature of around 175 C and be a dangerous machine.


text:
How can one demonstrate/assure safety for LRU's, CBAs, SoC's and other integrated modules?
Does anybody have experience with getting complex modules that were designed by others for common use, approved for incorporation in an airborne system that is at DAL A, B, or C and thus requires FAA approval?  I am doing research on the topic of how optimal the current approval guidelines are.
The question is of interest for LRU's (Line Replaceable Units), CBA's (Ciruit Board Assemblies, SoC (System on a Chip sunits) and other integrated technology modules.
If anybody out there has interacted with a DER and either found the means of demonstrating compliance to be sensible and practical, or can point out either gaps where potential errors could have snuck through or places where the approval process is impractical, I would appreciate it a lot.

You reference the FAA in the body of your question, but you added the [tag:easa-regulations] tag. Are you asking for both cases, or do you want information for one jurisdiction in particular?

Both or either would be very desirable to learn about.  The guidelines are almost identical, but if DERs interpret them differently that would be really excellent to know.

Not sure who voted this "too broad" but to me this question is extremely concise.  They are asking about certification viz a vi integration of very particular pieces of hardware.  It's a narrow field, and (assuming someone here actually has experience in it), it should be more than answerable.

@JayCarr I didn't, however I think that this should focus slightly, in that it should ask about either FAA or EASA requirements.  In fact, asking two different questions (one for each) would probably be best, because it is very likely that someone will have experience with one or the other, but not both and the answer is likely to be different since it is asking about a very complicated regulatory environment.

Yes, I've had some experience in dealing with complex hardware certification both with DERs and with FAA ACOs.  For the last 15 years or so, the process has been well defined as both FAA and EASA have adopted RTCA DO-254 Design Assurance Guidelines for Airborne Electronic Hardware.
I haven't run into many cases where there are any meaningful difference in interpretation of the guidelines, especially when discussing internally developed components.  There are some differences in what a DER/ACO will accept when you attempt to use commercial off the shelf (COTS) components.  DO-254 section 11.2 covers the use of COTS components but as it points out, the issue is lack of design data from the developer/manufacturer.  So coming to agreement on what is acceptable for these cases is highly variable depending on the DAL required and the available data.
For higher DAL levels it's getting harder and harder to get approval for COTS. You also have to deal with the fact that COTS parts may go through significant design changes on a regular basis.  That will impact your ability to maintain a single configuration.  Every part change has to analysed for impact and the configuration and certification updated.  That constant churn can quickly overcome any savings in procurement costs.
As to the more generic question of consistency between ACOs and DERs, it's an ongoing discussion within the FAA.  They want consistency but they don't want to to be so restrictive that all decisions get made at headquarters.  Every DER  or ACO I've met has had their individual biases and technical areas where they are comfortable.  So in that sense, there's always a bit of luck in getting one that sees things your way.  I don't think that will ever change.

The main difference that I am aware of between the FAA and EASA in regards to applying DO-254/ED-80 to Airborne Electronic Hardware is that the FAA applies it to custom micro-coded hardware (FPGAs, ASICs, PLDs, etc.) AC 20-152. EASA looks to also apply it to equipment (LRU, IMA modules) and circuit board assemblies Section 7 of EASA CM_SWCEH-001 Development Assurance of Airborne Electronic Hardware, albeit at DAL D.
Both agencies apply the actual DO-254/ED-80 process in the same manner
As far as COTS components are concerned, it is going to highly depend on a variety of things:

The design assurance level of the overall product or main Simple/Complex Electronic Hardware component
The functions the COTS components performs in the hardware
The available design data (or lack therof) for the COTS component
The DER/ACO you are working with

authors: Александра Лузина


text:
Why wasn't a scramjet used for the Concorde?
Why didn't Concorde use a scramjet engine for supersonic flight, but it is used in the Airbus and Skreemr hypersonic flight concepts to achieve supersonic speeds?

The scramjet has a little problem: How do you start it, and how do you fly before Mach 4 is achieved? In the video the SJY61 ramjet test engine and its support system are first carried by a B-52 to Mach 1 and 50,000 ft, released and immediately accelerated by a solid rocket engine up to Mach 4.5, at this point the booster is jettisoned, and the SJY61 scramjet is actually fired :-)

Were there even working scramjets when the Concorde was designed?  Wikipedia thinks the US didn't test one successfully until 2004.  The Russians apparently had one in the '90s, but either is decades too late.

TIL: B-52s can hit Mach 1!  Thanks, @mins!  :)

@FreeMan: At least M 0.91.

A supersonic ram jet (scramjet) requires a fuel with a very high flame speed, so the combustion doesn't take place after the fuel-air mixture has left the engine. Aviation fuel would be completely unsuitable, and only hydrogen gives acceptable results. The low density of gaseous hydrogen, the storage problems associated with cryogenic hydrogen and the creation of a hydrogen infrastructure would had created tremendous problems for the Concorde development.
A scramjet is like wing sweep: It is best avoided if possible, but necessary if you want to go really fast. For the scramjet the speed above which it makes sense is Mach 4 or 5, and Concorde was designed for Mach 2.

While not a scramjet, the J58 of the SR71 operated in similar conditions - very high temperatures - which necessitated the use of the very pricey JP7 fuel, and the need for an injection of TEB to ignite the fuel - the characteristic green glow seen when an SR71 fires afterburners. Ben Rich describes a project to power the earlier A-12 Oxcart with hydrogen to increase range, but it was abandoned as the minimal range increase didn't offset the difficulties in using hydrogen as an aircraft fuel.

Agree, @Peter Kampf, scramjet not practical for M~2. However, a comment on "only hydrogen gives acceptable results."  The X-51A and HiFire-2 are examples of hydrocarbon fueled scramjets. Point being is there are tradeoffs between fuel types. H requires cyrogenic storage, larger volume but has easier ignition. HC fuels are easier to handle, smaller volume, but harder to ignite.

The Skreemr at the present time is only an advertisement idea, so comparisons are not really meaningful.
Nevertheless, the difference with the Concorde is the expected range of speeds: at Mach ~2 a scramjet can hardly work (the air would be too slow at the combustion location).
All jet engines work on the same principles: compress (and slow down) the mass of incoming air in the compressor stage, heat it up in the combustion stage, let it expand (and accelerate) in the turbine/nozzle side.
If the compressor stage brings the air down below Mach 1, it is not a SCramjet anymore.

The Concorde was expensive enough working Mach 2, Hypersonic flight is crazy concept modern standards now.
One the drag equation, The drag of an object traveling thru air is proportional to the square of speed, then the power needed to overcome said drag is proportional to the cube of speed. If you were to double the speed you quadruple the aerodynamic drag. So a plane doing Mach 6 generates over 8 times more drag than a plane going mach 2 and must achieve an altitude of 150,000 feet which robs potential oxygen for air thirsty engines to overcome that drag, it also doesn't permit rapid altitude transitions as you go up and come back down.
At an altitude of 150,000 feet, the views sure are pretty, but risk exposure of crew/passengers to many times rate of cosmic rays and space borne radiation.
The SR-71 burned 12,000 gallons of fuel to fly a mere 2500 miles.
Aerodynamic drag, also generates another problem; air friction, and friction means temperature. To overcome when you have airplanes pushing hypersonic threshold required fuselage skins made of advanced and EXPENSIVE alloys that could withstand these temps. One was Inconel, a special alloy that even today costs 15 dollars a pound. Worse Inconel has a density nearly 9 grams per cubic centimeter on par with steel and 4x denser than aluminum; that makes a very heavy aircraft skin

authors: محمد غالب حُميد


text:
What happens to the fuel lines when a jet engine falls off?
Going off this question, what happens to the fuel lines to the engine when it falls off? Does it automatically shut off or do the pilots have to manually do it?

The scary thing is that your fuel consumption per hour goes up when the aircraft sheds one engine and nothing is done to shut off the fuel lines. Normally, the fuel pump pushes more fuel than needed towards each engine, and a second line routes excess fuel back. When the engine breaks off, the return line is also interrupted.

@PeterKämpf: On the B737 NG the return line starts at the hydromechanical unit, before the shutoff valve. The line which is severed is the HP one going from the valve to the engine. See page 12 on this schematic.

Engine separation won't cause automatic closure of valves, but the resulting low pressure will illuminate lights (including the Master Caution light) on the panels and display messages on the displays.
The pilots will have to react to the engine separation, the same way than for an engine fire or severe malfunction. This non normal procedure includes shutting down the fuel line by setting the engine start lever to CUTOFF or triggering the fire bottles on the affected engine.
There is a spar fuel valve (or fuel shutoff valve) fixed to the wing and to the fuel tank, which stays on the wing in case of separation. This valve is to prevent leaks due to a broken line. As the hydraulic power may be missing after the engine damage or separation, the valve is controlled by an electric motor with a backup battery and a double wiring redundancy.
Example on the the B737 NG:

(Shut-off valves framed in purple, source)
Non-Normal checklist used: ENGINE FIRE or Engine Severe Damage or Separation (NNC 8.2 of the Quick Reference Handbook).

(Click to enlarge, source)

Do you mean 737 NG?

Of course. Thanks

"the resulting low pressure will illuminate lights (including the Master Caution light) on the panels and display messages on the displays." Is there a hey, your engine fell off! light? I've heard of situations like that where the crew had no idea that the engine actually came off.

I'm not aware of any automatic fuel shutoff valve in case of engine seperation. The pilot has to manually close the fuel shutoff valve to prevent fuel loss. From b737.org:

Engine separation is an extremely rare event. ... It is important to use the fire handle to close the spar valve and prevent a massive overboard fuel leak; refer to the airplane flight or operations manual for specific procedures.

Also, see here.


text:
How do you handle frost on a plane?
If you plan to fly on a cold morning and there is frost on the plane, what needs to be done?
Do you have to remove the frost from the windows? wings? tail? fuselage?
How should you remove a thick layer of frost?
Can you rub the frost until it's smooth and take off?

...on small planes, beyond a certain point (what I can knock out in 15-20 minutes with a spray bottle of de-ice solution) I usually roll my eyes, curse the weather, and go across the field to the coffee shop to wait until it gets warmer :-)

Related: How NOT to handle frost on a plane!

Polishing frost is a perfectly acceptable practice (regardless of FAR's). I remove frost from windows, broom the wings and tail surfaces - check the undersides. Polish the fuselage if your feeling energetic. Take-off at a higher airspeed than normal.

Large aircraft operators are prohibited under FAR 91 Subpart F from polishing frost smooth - they must remove all of it prior to takeoff. While light GA aircraft don't fall under this rule, it makes sense to comply with it. Our wings are just as susceptible to the reduction in lift and increase in drag caused by ice and frost. ref

You should definitely not attempt flight if there is frost on the windows that would affect visibility, or on any of the wings or flight control surfaces.  Frost accumulation on such surfaces can reduce the lift generated by your wings, possibly causing a crash on takeoff.
According to the NTSB, frost the size of a grain of salt, distributed as sparsely as one per square centimeter over a wing's upper surface, can destroy enough lift to prevent a plane from taking off.
The cheapest solution is to try to re-position the plane on the ramp so that the sunlight has a chance to melt it away.
You can also temporarily move the plane into a heated hangar until it melts, or ask the FBO to do so for you.  If the forecast is predicting a chance of such conditions the night before, you can usually call the FBO on the night before and ask them to move your plane into their hangar just for the night, in advance of your morning flight.
If you're really anxious to go, you can ask the FBO to apply a heated deicing solution to your plane, but be prepared to pay for it (it's priced by the gallon and the amount needed will depend on the size and amount of frost of your plane).  Not all FBOs will have deicing capabilities, particularly if the region does not commonly experience such conditions.

I bring a small spray bottle of TKS fluid with me, including a few towels. Spray it on, wait a minute, then wipe off the snow/frost with a towel.  You can clean up a 4-seater plane in 20 minutes or so.  Do NOT use hot water, as that may re-freeze in a BAD place as later.  I use TKS anti-ice fluid made by Davies - can get it in gallon jugs.

I don't know if you're in the US, but if so then by regulation you must remove it from all critical areas before flight, per 14 CFR 91.527:

§91.527   Operating in icing conditions.
(a) No pilot may take off an airplane that has frost, ice, or snow
  adhering to any propeller, windshield, stabilizing or control surface;
  to a powerplant installation; or to an airspeed, altimeter, rate of
  climb, or flight attitude instrument system or wing, except that
  takeoffs may be made with frost under the wing in the area of the fuel
  tanks if authorized by the FAA.

In practice, that really means removing it all, and I guess that other countries have similar rquirements. The NTSB has a detailed guide on ground icing where they say that it must be removed "by any means necessary" before flight. For light aircraft, the usual recommendation is to hangar the aircraft and let the frost melt off. But you need to ensure any moisture is completely removed before flying, otherwise it may re-freeze.
Larger transport aircraft (or any aircraft, in principle) are usually de-iced, which is a common sight at airports in winter. The FAA has an extremely detailed document if you're curious.

Just for the record, 91.527 is part of 14 CFR 91 Subpart F, which only applies to "Large and Turbine-Powered Multiengine Airplanes and Fractional Ownership Program Aircraft".  While this doesn't apply to most light airplanes, it is a very good practice to follow to ensure a safe flight!

Polishing the frost until smooth used to be a legally permitted way of handling the problem.  The regs have changed, because a very small amount of frost, polished or not, can seriously affect your aircraft's performance.  It must be removed!  POLISHING THE FROST IS NO LONGER PERMITTED.
However, if the frost is not on control surfaces, say on the top of the fuselage, it is ok to fly with it on.  (Unless of course you are flying a Piaggio or some other plane where the shape of the fuselage creates lift...)

Could you link to the reg?

See the answer above by Pondlife.

Pondlife's answer only applies to certain aircraft (though he doesn't note this, see Lnafziger's comment). Do you have a reference for other aircraft, such as a C172 operated under §91?

Sorry, I have been away for a while.  far

Of all the challenges in aviation, ice is probably the scariest, no matter the size of the airplane. It can ruin your day REAL fast if you don't deal with it properly. Bigger aircraft usually have better systems / support personnel to deal with it, but it still needs to be dealt with on smaller aircraft. If you're still on the ground, remove it completely. From every surface. Use deice fluid to get rid of it (or a heated hangar), and if the accumulation is such that it keeps returning quickly, anti-ice solution can work. But this level of icing should definitely factor into your No-Go decision.


text:
How can you identify an Airbus or Boeing from the inside?
How can you recognize a plane from the inside, when you are already sitting as passenger? In particular, is there a way to understand if you are inside a Boeing or an Airbus?

Look at the evacuation pamphlet in the seat back in front of you. It will also help you identify an Embrarer and other makes of plane.

look at the safety cards and listen to the captain's announces. It may provide the aircraft type.

If there is no window shade and just a button that changes the darkness of the window, it is definitely a Boeing 787.

I find that the row and seat numbers are under the overhead baggage compartments on Airbus planes.  I always have to hunch down and turn my head to see the row and seat numbers on Airbus flights.  Boeing, I can see the number while standing up straight.  Just look for the american guy craning his head to see the seat numbers, and you'll know you are on an Airbus.

Watch the engine cowling during the takeoff roll.  If it falls off, leaving the guts of the engine exposed, you're in an Airbus (specifically, an A320).

@Mark I thought I just watched an episode of Mayday where that happened to an A320 but now I can't find it. "a320 engine cowling falls off" has lots of results though :D

@Mark: interesting that you post that, less than a month after this.

if you are in economy in an A330 or A340 then the seating will be as in a 2-4-2 grid

@GianniAlessando I've reverted your last edit on this question as it does not substantially clarify what you're asking. If you are asking about interior features of the aircraft you have received an answer regarding those here.

There are many details to recognize, for example: The handle that locks the doors.

Image is a still from this video

Image source
Another way is to read the safety card, on them, you can read clearly if you are on a Boeing or Airbus, and on which type as well. The first picture is a typical Boeing's door, and the second, an Airbus'.
(source internet pictures from different types of handles)
On Airbus A32F, when the landing gear extends, the exit lights will turn on.
The cabin interior differs from company to company, however the cockpit is unique, but nowadays, passengers are not allowed to visit the cockpit during the flights.
If you seat on the seats, from where you can identify the winglet, they could give you some tips, most of the Airbus A32F have shark winglet, but it is changing, however, scimitar winglets are typical from New generation Boeings 737.

"There are many details to recognize": Could you add some more to your answer?

The handle doesn't lock the door. It is purely to pull the door shut. Also the big leaver doesn't either, that arms the auto deployment of the inflatables.

Look at the safety card in the seat pocket in front of you:

As a side note, it will be beneficial to read the safety card as well.

I may also ask the hostess. Clearly that's not the answer required for this question.

@GianniAlessandro Your original question was good, even if it did not express what you meant and did not get the type of answer you were looking for. I would recommend asking a new question, rather than editing your question at this point to substantially change the criteria.

I assume, we need to recognize a plane in the movie or some other context where the type is not simply written on the card in front of you.

This totally uninformative and useless answer has 35 upvotes? Seriously? O_O

@motoDrizzt From the perspective of an inexperienced passenger wanting to know more about the aircraft they are riding in, this answer gives what is one of the easiest and most accurate ways of making the determination. The safety briefing card is a mandatory item, and will differentiate between far more types than merely Airbus and Boeing.

@GianniAlessandro Aside from this answer, the question would really be too broad. Airbus and Boeing both make lots of different models of aircraft and each airline installs their own interior. An Airbus and a Boeing from the same airline will often look more similar on the inside than 2 Boeings or 2 Airbuses from different airlines. Some specific models have unique identifying features, but those are unique to individual models, not true for all aircraft from the same manufacturer. You'd need to ask which specific models you want to differentiate to get a meaningful answer other than this one.

When entering the plane have a look at the front door's frame. Airbuses have a sign showing when the door / plane was manufactured. I always check this sign just to know how old the plane is...
This placard is required by 14CFR45.11(g)

(g) The identification plate described in paragraph (a) of this
  section may be secured to the aircraft at an accessible location near
  an entrance for—
(1) Aircraft produced for—
(i) Operations under part 121 of this chapter,
(ii) Commuter operations (as defined in §110.2 of this chapter), or
(iii) Export.
(2) Aircraft operating under part 121 of this chapter and under an
  FAA-approved continuous airworthiness maintenance program; or
(3) Aircraft operating in commuter air carrier operations (as defined
  in §110.2 of this chapter) under an FAA-approved continuous
  airworthiness maintenance program.

I can't say this is something I've ever noticed. I'll certainly look for it next time I fly.

I've seen this placard on Boeings (737s at least) as well


text:
Where can I find the standards for airborne systems software design? Is there a central repository for this information?
In reading about software and equipment design for aircraft I'm finding a lot of references to various standards like "DO-178B, Software Considerations in Airborne Systems and Equipment Certification", but I'm having a hard time finding copies of these.
Is there a central repository or location where I can review or purchase these standards?

This question appears to be off-topic because it is about resource location. The document is not that hard to find in the RTCA online store or in the EUROCAE online boutique (as ED-12B).

@DeltaLima Those three comments together look like a pretty good answer!

in its current form this is almost a duplicate of these two questions.

possible duplicate of Is there any U.S. / FAA regulation that could apply for aviation software?

I don't think this is an exact duplicate of that question. The suggested original is asking about FAA regs dealing with software to do with flying, whether it runs on the aircraft or not. This question is specifically about software that runs on the aircraft, and it asks about relevant standards, not regulations.

Many of these are Radio Technical Commission for Aeronautics (RTCA) standards.
You can get these documents from the RTCA website. They are provided free of charge to RTCA members, non-members have to pay.
Alternatively you can acquire the European equivalents from EUROCAE (RTCA DO-178B is ED-12B in the EUROCAE eShop).
If you want to be up-to-date (for example if you're building a new avionics system), you should buy the latest version of the standard, such as DO-178C / ED-12C, which is the latest edition of your example above (published in 2012).


text:
How to get a NOTAM on a Restricted Area?
Is there any online service to get restricted area NOTAMS?
For example how can I get NOTAMs related to R-2503-D (intermittent by NOTAM 24 Hrs in advance) on Los Angeles Sectional chart?
I found this website but I am not sure how to find by restricted area name.

Restricted areas are controlled by the appropriate controlling agencies.  They will be listed either next to the area on a WAC or SAC chart, on in the chart sideliners.  I don't think NOTAMS will be utilized for this information.

If you look at the legend it actually mentions "intermittent by NOTAM 24 Hrs in advance"